聚氨酯材料老化的化学与力学交互作用研究

The hydroxyl terminated polybutadiene (HTPB) based and fluorine-containing polyurethanes are good binders and energetic materials, widely used in propellants and aerospace industries. It has become an important area for research on aging and anti-aging of polyurethane materials. This research project focuses on aspects of the mechanism of aging of HTPB polyurethane and fluorine-containing polyurethane, as well as the effect of chemical aging on mechanical properties. This project is divided into three parts: (a) research on the mechanism of aging of HTPB polyurethane; (b) research on the mechanism of aging of fluorinated polyurethane; (c) effect of the interaction between chemical aging and the change of mechanical properties. The high level quantum chemistry method and molecular modeling technique will be used to study this project. According to a scientific technology scheme designed, we will solve the key problems of reasonably constructing the network structure of polyurethane and the molecular structure of aging polyurethane. This project is featured with a combined experimental and theoretical study on aging problem of urethane materials, which relies on the hardware and software platforms of Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences. This project aims at revealing general laws of the effect of interaction between chemical aging and the change of mechanical properties of polyurethane materials, proposing aging mechanism of polyurethane materials and corresponding anti-aging method. The theoretical results will help to explain aging phenomena, and provide theoretical data in the process of modification and design of polyurethane materials. The applicant has a good working basis and working conditions, which can ensure that this project will be systematically carried out with reliable scheme, feasible technology and verifiable objectives over three years.

丁羟聚氨酯和含氟聚氨酯是很好的黏结材料和含能材料，在推进剂和航空工业中广泛使用。研究聚氨酯材料老化与防老化问题已成为聚氨酯学科的重要研究领域。课题研究重点关注丁羟聚氨酯和含氟聚氨酯的老化机理以及老化的化学和力学交互作用等几个方面，分为三个研究部分：丁羟聚氨酯老化机理研究；含氟聚氨酯老化机理研究；聚氨酯老化的化学与力学交互作用研究。通过高水平量子化学计算和分子模拟方法，按着科学的技术路线，重点解决构建合理的高分子网络结构和老化分子结构的关键问题。以深入的理论研究和实验相结合为特色，依靠中科院上海有机所优良的软硬件平台，揭示聚氨酯老化的化学与力学交互作用一般规律，提出聚氨酯老化失效机理和防老化方法，解释实验现象，为聚氨酯防老化改性设计及其在推进剂和航空材料中的应用提供理论支持。申请人有着很好的工作基础和工作条件，确保申请课题是方案科学、技术可行、成果可考的。整个课题分三年有计划有步骤地开展。

根据课题研究计划，开展了HTPB-IPDI聚氨酯的热老化机理研究。通过构建HTPB-IPDI交联网络的简化分子结构模型，并在B3LYP/6-311G(2d,p)理论水平上计算了一些特征化学键的均裂解离能（BDE）。计算发现与CH2相连的C-O键的BDE计算值最小，预示该化学键在HTPB-IPDI聚氨酯材料热老化过程中容易断裂分解，降解产物主要是CO2。与酯基相连的α-C-H键属于最弱的C-H键，推测该化学位点容易受到自由基或者O2的进攻而发生氢转移反应，是发生热氧老化或者光化学老化的特征点。热力学计算推测HTPB-IPDI聚氨酯另一个高温热分解途径是该材料降解为取代的环己烯、甲基氨基甲酸、甲胺、CO2等产物。通过对最易断键的C-O键热老化活化自由能的计算，发现其老化半衰期是温度的指数衰减函数，预示HTPB-IPDI材料随着温度升高呈加速老化趋势。通过分子动力学方法对HTPB-IPD聚氨酯材料热老化前后结构变化对材料力学性能的影响进行研究，模拟发现HTPB-IPDI随着老化释放CO2体系的密度随之降低，弹性模量和剪切模量逐渐降低，体模量和泊松比有所上升，表面材料的刚性增强，柔性减弱，力学性能显著下降。在丁羟聚氨酯分子中的不饱和C=C双键有很高的化学反应活性，很容易受大气中的O2、•OH和•OOH等氧化性组分进攻，发生氧化反应，是丁羟聚氨酯重要的氧化老化反应机理。系统研究了丁羟聚氨酯氧化反应体系，C=C与O2、•OH和•OOH发生氧化反应的反应机理。计算发现丁羟聚氨酯分子中不饱和C=C氧化产物主要有环氧化物和交联过氧化物，确定了丁羟聚氨酯分子中的C=C氧化反应的主反应。此外，对于丁羟聚氨酯分子中活泼氢受O2、•OOH氧化的机理研究，计算发现含有α-H基团的氧化产物主要有过氧化物、酮类化合物和醇类化合物，确定了丁羟聚氨酯分子中含有α-H基团发生氧化反应的主反应。